Wireless access technologies such as 802.11x and 3G/4G, each of which is fully familiar to those skilled in the art, have been providing steadily improving data rates at steadily reduced costs, thereby paving the way for ubiquitous, high-speed broadband wireless coverage. The biggest challenge in making this vision a reality, however, is to cost effectively connect all of the access points (e.g., cellular base stations) to the Internet using some backhaul technology. Current backhaul technologies such as T1 or DSL lines (each of which is fully familiar to those skilled in the art) are fast becoming a bottleneck as access speeds rise, and faster wired technologies such as T3 or fiber connections (also each fully familiar to those skilled in the art) can be expensive to lease or install in a number of scenarios.
With the technical improvements and standardization of long-haul, non-line-of-sight (NLOS) wireless technologies such as, for example, WiMAX (also known as 802.16d or 802.16-2004, and also fully familiar to those skilled in the art), the use of a wireless backhaul network is quickly becoming a cost effective alternative to wired interconnection-based technologies. The recent standardization of the WiMAX technique is expected to drive down prices of WiMAX-compliant hardware, making it possible for service providers to extensively deploy WiMAX-based backhaul links at competitive costs. The added benefits of a wireless backhaul include ease of deployment (i.e., since there is no need to run wires) and the ability to bypass an incumbent wireline carrier's networks. Furthermore, with spectral availability widening globally (especially, for example, in the 5 GHz range) standardized wireless backhaul equipment can now be deployed in a large number of locations.
Wireless backhaul networks will be useful to provide high speed Internet access to residential, small and medium business customers, as well as Internet access for WiFi hot spots and cellular base stations. (The WiFi standard communications protocol is also fully familiar to those skilled in the art.) Public safety services and private networks could also be advantageously built using wireless backhaul links. In particular, multihop wireless architectures for backhaul have the potential to provide ubiquitous, high-speed wireless access to consumers. (As is fully familiar to those skilled in the art, a multihop wireless architecture permits more than one wireless connection or “hop” from a wireless terminal to a wired “gateway.”) In principle, multihop wireless networks are easy to deploy and expand incrementally, can adjust to failures or changing traffic demands by reconfiguring backhaul routes, and can provide ubiquitous service, especially in areas with no installed wired base. Furthermore, multihopping allows one to reduce the distances over which the access points need to transmit on the backhaul links. This can help increase network throughput due to lower path loss and better spatial reuse.
FIG. 1 shows a sample of a one-hop wireless backhaul network (FIG. 1A) and an equivalent multihop wireless backhaul network (FIG. 1B). As can be seen in the figure, both networks connect the same ten access points to a single wired access point R. However, the above-described advantages apply to the multihop wireless backhaul network of FIG. 1B as compared to the one-hop wireless backhaul network of FIG. 1A.
Recent commercial deployments of such multihop wireless or “mesh” backhauls in the real world are beginning to demonstrate some of these advantages. However, several challenges remain in allowing multihop wireless backhaul networks to match the throughput and more particularly the delay guarantees of wired backhaul networks. As is well known to those skilled in the art, multihopping can help boost throughput, but the transmission of packets through the network must now be more carefully scheduled to reduce interference and maintain low delays over multiple hops. In particular, providing guaranteed rates while keeping end-to-end delays low is extremely important for any backhaul network that will carry delay sensitive traffic (such as, for example, Voice Over IP, video and interactive applications).